Microstructure cast strip in 0.1 mass% C steels containing phosphorus

Cast strips of 0.1 mass%C steels with phosphorus contents ranging from 0.01 to 0.2 mass% have been produced by using a twin drum type continuous casting machine, and their microstructures have been characterized. Fine dendrite structure in the strips provides a fine dispersion of the segregated phosphorus regime. Phosphorus addition changes the alpha grain structure dramatically and decreases the gamma grain size. The EPMA (Electron Probe Micro Analyzer) mapping and the diffusion analysis of phosphorus in the gamma phase indicate the presence of a retained delta phase in the austenite temperature. The pinning effect of the delta-ferrite on the gamma-grain growth must be kept in the temperature range of the rapid gamma grain growth. The balance of strength and ductility for the cast strip is improved as the phosphorus content increases.